1. Field of the Invention
This invention relates to optical communication systems. More particularly, this invention relates to a switch that changes state in response to the detection of electromagnetic radiation of a frequency other than the frequency of a data signal being transmitted through the switch.
2. The Prior Art
Loop-back, in which a signal is sent down one optical fiber and returned on another optical fiber, is a common method of testing for the continuity of an optical communications channel. Most conventional loop-back systems employ a switch at the remote end of the channel that must be manipulated by a control signal transmitted over a separate control channel.
Having a separate control channel for activating a loop-back switch adds cost and complexity to the communications system. Furthermore, if a discontinuity were to develop in the control channel, then the ability to control the loop-back switch would be impaired.
Nowhere does the prior art disclose an apparatus that uses a light of a control wavelength, different from the data wavelength, to control a remote optical switch.